Magnetron sputtering target for magnetic materials

ABSTRACT

A target for physical-vapor deposition (PVD) and methods for depositing magnetic materials are described. Radio frequency (RF) or direct current (DC) power is introduced into the chamber through the target to produce plasma. The planar magnetron system is chosen for its high deposition rates. Since the permanent magnets are behind the target in the traditional system, a magnetic target interferes with the required magnetic fields on the target. To eliminate this problem permanent magnets are arranged on the surface and a magnetic target is used as a part of the magnetic circuit. Strong magnetic fields on the target can now be maintained for high deposition rates. The permanent magnets may be covered by a relatively thin, suitable protective-film or by a film of the same material as the target.

FEDERALLLY SPONSORED RESEARCH

[0001] Not Applicable

SEQUENCE LISTING OR PROGRAM

[0002] Not Applicable

BACKGROUND—FIELD OF INVENTION

[0003] This invention relates to physical-vapor deposition (PVD) andmethods for depositing magnetic materials with planar magnetronsputtering system

SPUTTERING DEPOSION OF PRIOR ART

[0004] Sputtering is a method of physical-vapor deposition (PVD) thatinvolves the removal of material from a solid cathode by bombarding itwith positive ions from the discharge of a rare gas such as argon (Ar).The cathode can be made of a metal or an insulator and in contrast tothermal evaporation, complex compounds such as high-temperaturesuperconductor (HTS) materials can be sputtered with lesschemical-composition change. Sputtering is often done in the presence ofa reactive gas, such as oxygen or nitrogen, to control or modify theproperties of the deposited film. The following are some of theadvantages of the sputtering method:

[0005] Environmentally benign process systems compared with chemicalprocesses

[0006] Choice of a wide range of deposition rates for the best growthconditions

[0007] Control of a wide range of oxygen or nitrogen levels in thedielectric films

[0008] Use of oxide or non-oxide targets (reactive sputteringdeposition)

[0009] Use of single or multi co-sputtering processes

[0010] Growth of c-axis oriented layers on amorphous substrates

[0011] Growth of not only c-axis but also a-axis oriented layers on asingle-crystalline substrate

[0012] The sputtering deposition system provides high-densitynucleation, which has not only a c-axis but also an a-axis orientationon single-crystalline substrates. This process is ideal for the first,or nucleation step; however, it fails to make a single crystal becauseof the difficulty to maintain thermal-equilibrium growth-conditions athigher temperatures necessary to grow a single crystal. Ref (1)

BACKGROUND OF THE INVENTION

[0013] The planar magnetron system is simple and provides highdeposition rates from a simple flat target. The conventional system haspermanent magnets behind the target that provide strong magnetic fieldson the target. The magnetic fields confine high-density plasma to thetarget. The plasma on the target enhances the deposition ratedramatically. If it is a magnetic target, however, magnetic propertiesbypass the magnetic fields. Hence magnetic fields on the target will begreatly reduced. Magnetic materials cannot be deposited effectively witha conventional planar magnetron system.

[0014] Magnetron systems are very good for Physical Vapor Deposition(PVD) systems as a material source to be deposited because depositionrates are high and excess electron bombardment of the substrate isreduced. Ref (2) The planar magnetron generates magnetic fields throughthe target. The strong magnetic field on the target confines thehigh-density plasma causing target erosion. The conventional target willbecome thinner as erosion advances and magnetic fields on the erodedareas become stronger. The erosion profiles become deeper narrow rings.The stronger magnetic field accelerates erosion. It creates a narrow,deeper channel. This effect leads to a shorter target life and affectsthe uniformity of the deposited film on the substrate. The targetutilization rate is also lower. To partially solve this problem, costlyrotating magnets are required. The rotating magnets act as a magneticbreak. This requires a significantly high power motor and excess heatgenerated on the target becomes a problem.

[0015] In the conventional system, magnetic fields are introducedthrough the target so that very large, strong magnets are required toprovide sufficiently strong magnetic fields on the target. Although athicker target results in a longer life, even stronger magnets are thenrequired to provide adequate magnetic fields on the target.

SUMMARY OF THE INVENTION

[0016] 1. The new magnetron-sputtering target has the magnets on thesubstrate-facing surface of the magnetic target rather than behind thetarget so that strong magnetic fields can be applied to the targetsurface with smaller magnets.

[0017] 2. Magnets to be exposed in the plasma may be coated with propermagnetic and/or non-magnetic materials by plating them on the magnetsurfaces. This practice is already in use with the conventionalmagnetron systems to prevent corrosion.

[0018] 3. The required magnets are very small and provide strongermagnetic flux on the target. Magnetic circuits can be designed moreprecisely for these front-mounted magnets than for those on the back ofthe target.

[0019] 4. Better magnetic circuit design eliminates the need for rotatedmagnetic fields and provides a more uniform deposit.

[0020] The permanent magnets will be placed on the magnetic targetrather than behind the target. The major erosion area is between theopposite polarities permanent magnets that are on the magnetic target.The permanent magnets erode very little, but they may be coated withsuitable materials to prevent cross contamination. In thisconfiguration, permanent magnet strips or rings form magnetic fieldsdirectly on the target, where as the conventional planar magnetrongenerates magnetic fields through the target. My innovative magneticcircuit design does not limit the thickness of the target and magneticdistribution is far better than that of the conventional design. Therequired permanent magnets are smaller and much less inexpensive.

[0021]FIG. 1 shows a typical planar magnetron in a vacuum chamberincorporating this new target design. All permanent magnets have apolarization from top to bottom and the target provides a common basefor the magnetic circuits set up by the permanent magnets. Strongmagnetic fields between opposite permanent-magnet polarities trap andconfine the high-density plasma. This high-density plasma on the targetenhances target erosion and as erosion advances, the magnetic fieldstend to be weaker. This results in wider erosion profiles. Since themagnetic circuits are directly exposed rather than through the thicktarget, smaller permanent magnets can be used. The smaller magnets makeit possible to achieve more efficient erosion patterns. This leads to amore uniform sputtering source without rotating magnets or magneticfields. Although the rotating magnetic assembly improves depositionuniformity, the rotation reduces the magnetic field on the target,generates more heat due to magnetic break effect, hinders idealelectrical feeding system, and triggers plasma instability, includingabnormal arc discharges.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a schematic view of a sputtering system having a vacuumchamber 10 within which a target 15, a substrate 12 and a magnet 16 of amagnetron array are set up according to my invention.

DRAWINGS Drawings Figures

[0023] In the drawings, closely related figures have the same number butdifferent alphabetic suffixes.

[0024]FIG. 1 schematic diagram of sputtering system

[0025]FIG. 2 prior art target assembly

[0026]FIG. 3 simple target concept diagram of new invention

[0027]FIG. 4 coated permanent magnet, section

[0028]FIG. 5 section diagram of invention, concept 1

[0029]FIG. 6 section diagram of invention, concept 2

[0030]FIG. 7 section diagram of invention, concept 3

[0031]FIG. 8 more realistic magnet arrays, see from substrate side

[0032] Reference Numerals in Drawings 10 vacuum chamber 11 to vacuumpump 12 substrate 13 cooling water in-out lets 14 water jacket 15magnetic target 16 permanent magnet 16A permanent magnet, large ring 16Bpermanent magnet, small ring 16N permanent magnet, north pole facessubstrate 16S permanent magnet, south pole faces substrate 17 plasma 18gas inlet 19 insulator-vacuum seal 20 magnetic base plate 21 prior arttarget 23 surface coat 26 major erosion area

DETAILED DESCRIPTION

[0033] The sputtering system in which my magnetron array is mounted isshown in FIG. 1. The sputtering process occurs in a vacuum chamber 10containing a target 15 of material to be sputtered onto a substrate 12which receives a thin film coating of the material deposited from thetarget. Sputtering is a method of physical vapor deposition thatinvolves the removal of material from a solid cathode or target 15 bybombarding it with positive ions from the discharge of a rare gas suchas argon (Ar) supplied from the gas inlet 18. The cathode can be made ofa metal or an insulator and is heated by ion bombardment or dischargeenergy. The excess heat build-up must be removed by a water jacket 14with continually circulating water through in/outlet 13. The targetassembly is built into the chamber by means of an insulating ring and avacuum seal 19. The substrate 12 is often a wafer on which magneticcomponents are fabricated, but it can also be a microelectronic wafer,optical element or other structure having a surface to be coated.

[0034] The conventional planar magnetron sputtering assembly is shown inFIG. 2 (PRIOR ART). The magnetic field is provided by permanent magnets16 mounted on the magnetic base plate 20 behind the target. The field onthe target confines the high-density plasma 17. The plasma on the targetenhances the deposition rate dramatically. If it is a magnetic target,magnetic properties bypass magnetic fields. Magnetic materials cannot bedeposited effectively with a conventional planar magnetron system

[0035] My invention involves the location of the magnetic array, thepreferred configuration of which is shown in FIG. 3. The target portionof the sputtering system consists of an array of permanent magnetsfastened to the target surface facing the substrates at an appropriatedistance from the substrates.

[0036] The magnet 16A and 16B to be exposed in the plasma may be coatedwith suitable magnetic and/or non-magnetic materials 23 by plating thesematerials on the magnets as shown in FIG. 4. This practice is alreadyused in the conventional magnetron system to prevent corrosion.

[0037] Three variations of target assemblies are shown in FIG. 5, FIG. 6and FIG. 7. The simplest application of all is that of two rings ofmagnets attached to the magnetic target by their own magnetic forces asshown in FIG. 5. The back of the target is bonded to a water jacket 14for cooling purposes. FIG. 6 shows the magnets partially embedded in amagnetic target. Non-magnetic materials may be sputtered by fasteningthe target to a magnetic base plate. The surface of the target may bemodified according to magnetic properties of the target 15, permanentmagnets, gas composition and pressure, operating power, and the spacingbetween the north 16B and south 16A magnets mounted on the surface ofthe target. FIG. 7 shows a magnetic target with a machined surface,which, when exposed to the plasma, enhances the thin film uniformity asthe target erodes more uniformly leading to longer target life.

[0038] Using a micro-pattered magnetic circuit as shown in FIG. 8 willmaximize performance of the new target assembly. The small magnets areembedded or in the guiding trenches and form micro-patterns of magneticfield between north 16N and south 16S poles on the magnetic target 15.The plasma is confined in the magnetic field and micro-erosion patterns26 will be formed. The erosion patterns are uniformly distributed sothat material supply will be uniform. The substrate can be closer to thetarget. Multiple benefits include high deposition rate, minimum chambercontamination, and better deposition uniformity. The semi-directexposure of the permanent magnets provides the best uniformity ofmagnetic field over the whole target area.

I claims:
 1. The permanent magnets in this magnetron sputtering systemare fastened to the magnetic target surface facing the substrates at anappropriate distance from the substrates.
 2. The magnets may be coatedwith suitable materials such as the target material or anon-contaminating material with the deposited film. Since the surface ofthe magnets erode little and may be coated, no-contaminating materialsare deposited on the substrate.
 3. Since the permanent magnet circuit islocated on the surface of the target and is directly exposed to theplasma rather than through the thick target, the required permanentmagnets are smaller and less expensive than those mounted on the back ofthe target.
 4. The smaller magnets make it possible to design suitableerosion patterns. The magnetic circuit design is simpler withsurface-mounted permanent magnets.
 5. The erosion profiles become wider,rather than deeper rings, so that the utilization of the target isenhanced and the life of the target is increased.
 6. The permanentmagnets are held on target by their own magnetic force, or they can bebonded on the target. They can also be held on mechanically or by acombination of methods.
 7. My innovative target assembly does not limitthe thickness of the target and it provides better target-coolingcapability.
 8. A non-planar, machined surface of the target (FIG. 7) maybe used for a variety of applications.
 9. The small erosion areasproduced are ideal for very small targets.
 10. Electrical connectionsare easier and an ideal power feeding system can be designed.
 11. Duringdeposition, the large amount of heat associated with the plasma drivingpower can be removed effectively with the new invention. There is nolimitation on the thickness of the target assembly, including the waterjacket since the thickness does not hinder the magnetic field strengthon the target.
 12. Better magnetic circuit design provides betterdeposition uniformity and better erosion profile of the target withoutthe need for rotating magnets. The stationary magnetic source provides astable plasma with no abnormal arc discharge.
 13. The rotated magnets inthe conventional target work as a magnetic break which requires a highpower motor causing target heating. Without the rotating magnets, plasmapower feeding and target cooling design can be idealized. Better coolingdesign makes it easier to remove heat from the target.
 14. Fine erosionpatterns can be achieved with small magnets so that the uniformity ofthe deposited film and utilization of the target are greatly improved.The precisely aligned magnets provide uniform magnetic flux over theentire erosion area, as opposed to the magnetic pole pieces. These polepieces can be effectively used only with the simplest erosion patternsare acceptable. These pole pieces with the complex patterns distributethe magnetic flux unevenly. The fine patterned erosion areas in myinnovative design make it possible to reduce the distance between thetarget and the substrate. This leads to a higher deposition rate withmore material deposited on the substrate and less on the chamber walls.15. A non-magnetic target may be used by laminating it to a magneticbacking plate.